With the application potential of dynamic tunability of electromagnetically induced transparency (EIT) effect group delay in optical communication, the EIT effect has been widely studied in recent years. To improve the group delay performance, we propose a structure of nanobeam cavity-coupled microring resonator. Meanwhile, to realize its application value through EIT effect regulation, we integrate two layers of graphene into the microring resonator structure assisted by the one-dimensional photonic crystal nanobeam cavity, and the active EIT effect regulation is achieved by adjusting the Fermi level of graphene. During changing the Fermi level of graphene, the active regulation of its group delay is also realized. Additionally, since the harsh experimental conditions such as extremely low experimental temperature, high-intensity light source, and huge experimental equipment should be met to achieve EIT in the quantum field, EIT development is greatly limited. With the development of photonics, realizing the EIT effect in photonics will avoid harsh experimental conditions and accelerate the research on the EIT effect. Whether the EIT effect can be realized in a simple and compact device is a problem worth studying.

There are two main research methods employed in this thesis, including the finite difference time domain (FDTD) method and the three-level atomic system research method. The three-level atomic system research method is the theoretical physical mechanism analysis of the EIT effect in the device. In the proposed system, the nanobeam and the microring resonator are the bright mode and dark mode respectively. In the three-level atomic system, the bright mode is considered the excited state, the dark mode is the metastable state, and the incident wave without any excitation is the ground state. The EIT effect arises from the mutual excitation between the three energy levels, which are direct and indirect. Since the phase difference occurs when there are transitions among different energy levels, the phase difference between direct and indirect excitation is π. This can be verified from Fig. 4, and the FDTD method is adopted to simulate the device. The main performance is the simulation of the output line type of the EIT effect when the Fermi level of graphene is changed. Additionally, the influence of microring radius and coupling distance on the EIT effect is simulated, and the switching regulation of the EIT effect is realized by changing the microring radius and coupling distance. Finally, the FDTD method is utilized to simulate the sensing characteristics and slow light effect of the proposed structure. In the study of the slow light effect, the Fermi energy level change of graphene realizes the group delay regulation.

In this thesis, the coupling structure of a one-dimensional photonic crystal nanobeam cavity and a slot-type microring resonator is adopted, and two layers of graphene are integrated into the microring resonator (Fig. 1). The nanobeam cavity and the microring resonator are coupled as the bright mode and dark mode through near-field coupling, and destructive interference occurs to result in EIT effect. The bright mode in the nanobeam cavity is continuous, while that in the microring resonator is discrete (Fig. 3). By changing the Fermi level of graphene, the switching regulation of the transparent window can be realized in Fig. 6, and the Fermi level change also realizes the regulation of group delay regulation in Fig. 10. Equation (1) indicates that the increasing Fermi level of graphene leads to rising graphene conductivity and metallicity. Meanwhile, Fig. 2(b) reveals that when the Fermi level of graphene increases, the graphene loss decreases. These are the reasons for regulating the transparent window switch. In this thesis, when explaining the physical mechanism of the EIT effect, the three-level atomic system theory is introduced to take incident light, nanobeam cavity, and microring resonator as ground state, excited state, and metastable state respectively. In changing the coupling distance and radius of the microring resonator, the switching regulation of the transparent window is also realized (Fig. 8). because under the increased coupling distance, the near-field coupling between the nanobeam cavity and the microring resonator will not occur, which will close the transparent window. Equation (4) indicates that the radius is small, the microring resonator wavelength does not resonate between 1515 nm and 1525 nm, and the incident wave can only excite the bright mode, with the closed window.

We propose a coupling system between the nanobeam cavity and microring resonator, which produces an EIT-like effect due to near-field coupling between bright and dark modes and destructive interference. In this thesis, the three-level atomic system combined with the photonic crystal nanobeam cavity assisted microring resonator (PCN-MRR) structure is adopted to explain the physical mechanism of the EIT-like effect. Additionally, a numerical EIT effect model is built with the internal losses of the structure only considered. While regulating the EIT effect, this thesis realizes the dynamic tuning of the EIT effect by integrating two layers of graphene into the microring resonator. The three-dimensional finite difference time domain (3D-FDTD) simulation shows that the change of graphene Fermi level can complete the on-off regulation of the EIT effect at a specific resonant wavelength, and the position of the EIT-like window does not change with the Fermi level. The electric field distribution further shows that the graphene metallicity change plays a key role in EIT effect control. Finally, our research on sensing characteristics and delay characteristics of the structure shows that the sensitivity is 614.4 nm/RIU and the factor of quality (FOM) is 370.8, with a group delay of 7.1 ps and a group index as high as 895. Thus, it has application prospects in the sensing field and the research on slow optical devices.